There are various types of organic pollutants that mostly comprise of human waste (night soil), animal waste, food and chemical industry wastes. These, if discharged to aquatic bodies are subjected to decomposition by natural microbial population which consumes the dissolved oxygen of the surroundings resulting in disturbance of aquatic flora and fauna. Among these wastes human waste is of high concern because of its aesthetic and environmental nuisance. Its deterioration starts even before it is discharged from the human body. Besides leading to organic pollution, it is a store house of pathogens and is responsible for various water borne diseases such as cholera, jaundice and typhoid.
Historically, humans used to defecate in open areas where it was left for drying/natural degradation. Subsequently, the human waste was physically transported to an isolated area earmarked for its natural degradation which was not only generating off odorous compounds but also polluting and contaminating the natural surroundings. With the development of civilization, researchers are continually searching for newer methods for safe disposal of human waste. At present there are various options being practiced in various parts of the world, which include physical transportation, chemical and biological treatment (U.S. Pat. No. 5,580,457). Transporting of wastes from high population density is a costly affair because of the high cost of land in the adjoining areas and operational cost associated if waste is removed to remote locations of low cost. This is particularly problematic if liquid waste is to be transported to the disposal site. Incineration of the waste is facing increasing public resistance due to the release of noxious gases and high costs. In general chemicals used to treat the waste do not completely degrade the human waste and as a result add to the environmental pollution.
Biodegradation is considered to be the most preferable way of treating the waste because of its self-sustainability, cost effectiveness and eco-friendliness. It is carried out in two different ways: aerobically and an aerobically. Aerobic process employs bacteria, which have ability to use oxygen in energy generation. Because of this ability the addition of oxygen or air to a bioreactor/digester can increase the aerobic population rapidly. This increase in population results in increased rate of biodegradation but unfortunately aerobic population becomes the sludge/pollutant. This sludge must be removed prior to discharge of treated material into the environment. Moreover, aerobic process is an energy intensive process requiring energy for aeration. On the other hand, anaerobic process employs bacteria, which grow strictly in the absence of air/oxygen. These bacteria are inhibited by oxygen rich environment. Anaerobic process does not essentially require the energy for its operation and the amount of sludge generated are comparatively very less because of lower biomass produced in absence of oxygen. The main products of anaerobic degradation include methane, carbon dioxide and hydrogen sulphide. Methane is primary component of natural gas and is readily combustible and thus can be burnt to produce energy without posing any significant environmental hazards. Moreover, anaerobic processes are known to inactivate the pathogens present in the human waste.
There are two kinds of human waste treatment systems. In the first kind all residences, businesses and the institutions in a municipality are connected through a network of sanitary sewers to a central sewage treatment plant. The second kind is the septic tank system mostly installed for single family where usually connection to a sewer is not available. However, there is no system/apparatus available, which can be used for human waste treatment in public carriers like train, bus, boat, aeroplane etc. for on-site treatment. The only option in these public transports is to collect the waste in a closed container and to transport it to the site of the treatment. To avoid the foul smell at the site of collection, chemicals are added to the collection which ultimately delay/retard the biodegradation process but create the problem at the site of biological treatment. In other words, this approach requires manpower, infrastructure and money for disposal of human waste generated in the public transport vehicles. Indian railway is the biggest public carrier in the world. Presently, there is no provision for storage collection and transportation of human waste generated during journey in the toilets is discharged on the rail tracks, thus creating aesthetic nuisance, foul smell, breeding place for insects and also the risks of various diseases because of the presence of pathogens. The situation is even more precarious at railway stations.
Therefore, there is a need of an apparatus (hereafter called as digester) which can be fitted onto a public transport vehicle and degrade the human waste for its safe disposal.